1. Field of the Invention
This invention relates to gas monitoring apparatus and more particularly to infrared remote gas-filter correlation (RGFC) sensors.
2. Prior Art
Reference is made to U.S. Pat. No. 3,976,884 issued Aug. 24, 1976 to Acton, et al and entitled "Method for Remote Monitoring of Gaseous Products" the subject matter of which relates to but does not anticipate the present invention. Further reference is made to a paper entitled "A Gas Filter Correlation Instrument for Atmospheric Trace Constituent Monitoring" authored by W. D. Hesketh, H. G. Reichle, W. A. Messey, T. V. Ward and H. H. Zwick and presented at the Fifth Annual Remote Sensing of Earth Resources Conference, Tullahoma, Tenn., Mar., 1976 which discloses related material but does not anticipate this invention.
It is necessary for health, safety and sound economic reasons that the loss of gaseous fuels, such as methane, from buildings, city-wide distribution lines and long-distance pipelines be detected promptly and accurately. Infrared remote gas filter correlation (RGFC), broadly, is not new.
The RGFC technique has been used in various forms for measuring from ground-based, aircraft, and space platforms trace gases in the atmosphere. These previous instruments used analog electronic signal processing and made certain assumptions about the effects of the background and atmospheric radiances in order to produce a readout of the gas concentration. In this invention digital electronics and microprocessors are used so that more accurate corrections for the background and atmospheric radiances can be made in real time.
For certain gases previous apparatus has been sensitive to reflected sunlight and to thermal radiation (i.e., radiation in the 2-4 micron region, approximately). This has been true for methane being detected at 3.3 microns. Interpretation of the daylight produced signal is very complicated and has restricted the use of the apparatus to the nighttime.
Therefore, it is one object of this invention to overcome the various problems encountered in the use of previous RGFC apparatus.
It is another object of this invention to provide RGFC apparatus which is blind to reflected solar radiation.
It is a still further object of this invention to provide a gas monitoring method and apparatus which is free of restriction to nighttime use and rapidly provides accurate results.